The invention relates to a non-pneumatic, structurally supported tire. More particularly, the invention relates to a non-pneumatic tire that supports a load with its structural components and has pneumatic tire-like performance capabilities to serve as a replacement for pneumatic tires.
The pneumatic tire has capabilities in load carrying, road shock absorption, and force transmission (accelerating, stopping, and steering) that make it the preferred choice for use on many vehicles, most notably, bicycles, motorcycles, automobiles, and trucks. These capabilities have also been highly advantageous in the development of the automobile and other motor vehicles. Pneumatic tire capabilities in shock absorption are also useful in other applications, for example, in carts carrying sensitive medical or electronic equipment.
Conventional non-pneumatic alternatives, for example, solid tires, spring tires, and cushion tires lack the performance advantages of pneumatic tires. In particular, solid and cushion tires rely on compression of the ground-contacting portion for load support. These types of tires can be heavy and stiff and lack the shock absorbing capability of pneumatic tires. When made more resilient, conventional non-pneumatic tires lack the load support or endurance of pneumatic tires. Accordingly, except in limited situations, known non-pneumatic tires have not found wide use as substitutes for pneumatic tires.
A non-pneumatic tire having performance characteristics similar to those of pneumatic tires would overcome the various deficiencies in the art and would be a welcome improvement.
A structurally supported, non-pneumatic tire in accordance with the invention includes a reinforced annular band that supports the load on the tire and a plurality of web spokes that transmit in tension the load forces between the annular band and a wheel or hub. Accordingly, a tire of the invention supports its load solely through the structural properties and, contrary to the mechanism in pneumatic tires, without support from internal air pressure.
According to an embodiment useful as a tire on a motor vehicle, a structurally supported tire includes a tread portion, a reinforced annular band radially inward of the tread portion, a plurality of web spokes extending transversely across and radially inward from the annular band toward a tire axis, and means for interconnecting the web spokes to a wheel or hub.
In a pneumatic tire, the ground contact pressure and stiffness are a direct result of the inflation pressure, and are interrelated. The tire in accordance with the invention has stiffness properties and a ground contact pressure that are based on the structural components of the tire, and, advantageously, may be specified independent of one another.
The structurally supported tire of the invention does not have a cavity for containing air under pressure, and accordingly, does not need to form a seal with the wheel rim to retain internal air pressure. The structurally supported tire does not, therefore, require a wheel as understood in the pneumatic tire art. For the purposes of the following description, the terms “wheel” and “hub” refer to any device or structure for supporting the tire and mounting to the vehicle axle, and are considered interchangeable herein.
According to the invention, the annular band comprises an elastomeric shear layer, at least a first membrane adhered to the radially inward extent of the elastomeric shear layer, and at least a second membrane adhered to the radially outward extent of the elastomeric shear layer. The membranes have a circumferential tensile modulus of elasticity sufficiently greater than the shear modulus of elasticity of the elastomeric shear layer such that, under an externally applied load, the ground contacting tread portion deforms from essentially a circular shape to a shape conforming with the ground surface while maintaining an essentially constant length of the membranes. Relative displacement of the membranes occurs by shear in the shear layer. Preferably, the membranes comprise superposed layers of essentially inextensible cord reinforcements embedded in an elastomeric coating layer.
The elastomeric shear layer is formed of a material, such as natural or synthetic rubber, polyurethane, foamed rubber and foamed polyurethane, segmented copolyesters and block co-polymers of nylon. Preferably, the shear layer material has a shear modulus or about 3 MPa to about 20 MPa. The annular band has the ability to bend from a normal circular shape while under load to conform to a contact surface, such as a road surface.
The web spokes act in tension to transmit load forces between the wheel and the annular band, thus, among other functions, supporting the mass of a vehicle. Support forces are generated by tension in the web spokes not connected to the ground-contacting portion of the annular band. The wheel or hub can be said to hang from the upper portion of the tire. Preferably, the web spokes have a high effective radial stiffness in tension and a low effective radial stiffness in compression. The low stiffness in compression allows the web spokes attached to the ground-contacting portion of the annular band to bend for absorbing road shocks and for better conforming the annular band to the irregularities in the road surface.
The web spokes also transmit the forces required for accelerating, stopping, and cornering. The arrangement and orientation of the web spokes can be selected to obtain the desired function. For example, in applications where relatively low circumferential forces are generated, the web spokes can be arranged radially and in parallel with the tire axis of rotation. To provide stiffness in the circumferential direction, web spokes perpendicular to the axis of rotation can be added, alternating with the axis-aligned web spokes. Another alternative is to arrange the web spokes oblique to the tire axis to provide stiffness in both the circumferential and axial directions. Another alternative is to orient the web spokes to be in an alternating oblique arrangement, that is, in a zig-zag pattern when viewed on the equatorial plane.
To facilitate the bending of the web spokes of the ground contacting portion of the tread, the spokes can be curved. Alternatively, the web spokes can be pre-stressed during molding to bend in a particular direction.
According to an embodiment of the invention, a structurally supported resilient tire comprises a ground contacting tread portion, a reinforced annular band radially inward of the tread portion, and a plurality of web spokes extending radially inward from the reinforced annular band, means for interconnecting the plurality of web spokes to a wheel or hub, the reinforced annular band comprising an elastomeric shear layer, at least a first membrane adhered to the radially inward extent of the elastomeric shear layer and at least a second membrane adhered to the radially outward extent of the elastomeric shear layer.
According to another embodiment, the invention comprises a structurally supported wheel-tire, comprising a reinforced annular band comprising an elastomeric shear layer, at least a first membrane adhered to a radially inward extent of the elastomeric shear layer and at least a second membrane adhered to a radially outward extent of the elastomeric shear layer, wherein each of the membranes has a longitudinal tensile modulus greater than the shear modulus of the shear layer, a tread adhered to a radially outer extent of the reinforced annular band, a plurality of web spokes extending substantially transversely across and radially inward from the reinforced annular band, and a wheel radially inward of the plurality of web spokes and integrated therewith.